logm: Fix overflow detection logic.
logm: Fix overflow detection logic.

Currently logm decides overflow happens even if g_logm_dropmsg_count is
zero. This is not correct. This patch add condition to overflow detection
logic to check g_logm_dropmsg_count is greater than zero.

Change-Id: Id792f044def1a68cd89ae01201dda88edc1131e9
Signed-off-by: EunBong Song <1a7e7e98e070490e67aa35ab67fbf9fdda8f48ac@samsung.com>

EunBongSong/TizenRT,EunBongSong/TizenRT,EunBongSong/TizenRT,EunBongSong/TizenRT,EunBongSong/TizenRT,EunBongSong/TizenRT